CN1045149C - Image signal correction device - Google Patents

Abstract

An image signal correction device, wherein an APL of a luminance signal is detected by an APL detection circuit (100), and a coefficient operation circuit (101) calculates a correction amount based on the APL. Next, an adder (102) adds the APL-based correction signal to the corrected luminance signal. On the other hand, the limiter circuit (104) limits the lower limit of the input luminance signal. Furthermore, the division circuit (7) divides the output signal of the adder (102) by the output signal of the limiter circuit (104), and corrects the input color signal based on the result. In this way, the correction of the color signal can be performed according to the APL value, and it is also possible to prevent excessive correction of the color signal at the time of low-luminance input.

Description

Image signal correction device

The present invention relates to an image signal correction device, which is used for gray scale correction processing (black level correction, gamma coefficient correction, etc.) The amount of correction for the signal, which corrects the saturation of the color signal to the optimum level.

In recent years, with the enlargement of color TV sets and the improvement of image quality, in order to make the image more vivid, an image signal correction device is used to pass the image brightness signal through a nonlinear amplifier for grayscale correction processing to enlarge the cathode ray. The dynamic range of the image on the tube (hereinafter denoted CRT).

Next, a conventional image signal correction device will be described. FIG. 6 is a block diagram of a conventional image signal correction device. In FIG. 6, 1 is a luminance signal correction circuit. The gradation of the input luminance signal is corrected and the corrected luminance signal is output. For example, a black level correction circuit, a gamma correction circuit, and the like. 2 is the contrast and brightness control circuit, which changes the bias level and contrast of the direct current (hereinafter referred to as DC) of the corrected luminance signal; 3 is the matrix conversion circuit, which produces a color signal according to the luminance signal and the color difference signal; 4 is the CRT . 5 is a color demodulation circuit, which demodulates the color carrier signal and outputs the color difference signal. 9 is an adder for adding the contrast control voltage and the color control voltage. 6 is a delay circuit, which adjusts the time difference between the delayed luminance signal output by it and the corrected luminance signal input to the dividing circuit 7 . 7 is a dividing circuit, which divides the delayed luminance signal by the corrected luminance signal, calculates the correction amount of the luminance signal, and outputs it as a color amplitude correction signal. 8 is a multiplication circuit, which uses the color amplitude correction signal to control the gain of the amplitude of the color carrier input signal, and outputs the color carrier correction signal. Here, circuits other than the CRT4 may be constituted by analog circuits or digital circuits, or may be constituted by a composite circuit of the two.

The operation of the image signal correction circuit configured as described above will be described below. Signal waveforms in various places are shown in FIG. 7 .

First, the luminance signal a is input to the luminance signal correction circuit 1, the gradation correction (black level correction, gamma correction, etc.) of the luminance signal is performed, and the corrected luminance signal b is output. Here, if the level of the luminance signal a is Ey, according to the standard of the NTSC system, such as formula (1):

Ey=0.3Er+0.59Eg+0.11Eb (1) where Er is the voltage of the color signal R (red), Eg is the voltage of the color signal G (green), and Eb is the voltage of the color signal B (blue).

Therefore, if the luminance correction amount of a certain point on the image is A, then the corrected luminance signal b is A×Ey. The corrected luminance signal b is input to the contrast/brightness control circuit 2, and its amplitude and DC bias level are adjusted by the contrast control voltage g and the luminance control voltage h, and then output as the output luminance signal c. As a result, assuming that the gain correction amount obtained by the contrast control is C, the output luminance signal c is A×C×Ey.

In addition, the luminance signal a is delayed in the delay circuit 6 so as to appear at the same time as the corrected luminance signal b input to the dividing circuit 7, and is output as a delayed luminance signal 1. Then, it is input to the dividing circuit 7 .

In the dividing circuit 7, the corrected luminance signal b is divided by the delayed luminance signal l to obtain the correction amount of the luminance signal. Here, if the amplitude of the delayed luminance signal l is equal to the luminance signal a, then the luminance correction amount A is shown in formula (2):

A×Ey/Ey=A (2) However, there is an operation error in the actual division circuit, and the result is α×A+β. If α≈1, B<<A, there is no problem.

The result is output to the multiplication circuit 8 as the color amplitude correction signal m. The amplitude of the input color carrier signal d is adjusted in the multiplication circuit 8 to match the color amplitude correction signal m. Under the NTSC system, if the input color carrier signal is En, the result is as in formula (3):

En=(Er-Ey)/1.14×cos(2×π×fs×t)

+(Eb-Ey)/2.03×sin(2×π×fs×t) (3)

Therefore, the color carrier correction signal n is A×En, that is, formula (4):

A×En=A×(Er-Ey)/1.14×cos(2×π×fs×t)

+A×(Eb-Ey)/2.03×sin(2×π×fs×t) (4)

Next, the color carrier correction signal n is input to the color demodulation circuit 5 for color demodulation, color tone control according to the color tone control voltage j, color control based on the calculated color control voltage k, and then output as a color difference signal e. In short, the color-difference signal e is obtained from the formula (4) after detection, and its form is as in the formula (5), and the color carrier signal n is multiplied by the contrast correction amount C.

R-Y composition: A×C×(Er-Ey)

B-Y composition: A×C×(Eb-Ey)

G-Y component: A×C×(Eg-Ey) (5) Here, the color control voltage k is obtained by adding the contrast control voltage g and the color control voltage i by the adder 9 . In short, color control is carried out together with contrast.

Next, the color-difference signal e is input to the matrix conversion circuit 3 together with the previous output luminance signal c, and the calculation is performed. The result is shown in formula (6).

R component: A×C×Ey+A×C×(Er-Ey)=A×C×Er

G component: A×C×Ey+A×C×(Eg-Ey)=A×C×Ey

B component: A×C×Ey+A×C×(Eb-Ey)=A×C×Eb (6) Then use each voltage of the obtained color signal f to drive CRT4 and display the image. (For example, refer to JP-A-01-344439).

However, in the above-mentioned existing structure, the luminance signal a is input as the denominator of the division circuit 7, therefore, when the level of the luminance signal a is a black level, that is, a level close to 0, the division result is close to infinite Large, therefore, overcorrecting the amplitude (saturation) of the color signal.

Also, since the color signal correction has nothing to do with the average luminance level (hereinafter referred to as APL), there is a problem of conspicuous noise when a dark (low APL) image is input.

The present invention solves the above-mentioned problems, and its purpose is to provide an image signal correction device. When the input luminance signal a is approximately 0 level, no signal below a certain value is input to the denominator of the division circuit 7, thereby preventing color correction. Signal overcorrected.

Another object of the present invention is to provide an image signal correction device, which detects the APL, and controls the correction of the color signal according to the correction amount of the luminance signal and the APL, thereby reducing the color noise of an image with a low APL (dark).

An image signal correction device of the present invention to achieve the above object includes an APL detection circuit, a coefficient calculation circuit, an adder, a limiter circuit, a division circuit, a multiplication circuit, and a coefficient control circuit.

Another image signal correction device of the present invention includes an APL detection circuit, a coefficient calculation circuit, first and second adders, a division circuit, and a multiplication circuit.

Another image signal correction device of the present invention includes an APL detection circuit, a coefficient calculation circuit, a limiter circuit, a first and a second division circuit, an adder, a multiplication circuit, and a coefficient control circuit.

Yet another image signal correction device of the present invention includes an APL detection circuit, a coefficient calculation circuit, first and second adders, first and second division circuits, and a multiplication circuit.

With the above structure, for the luminance signal input as the denominator in the division circuit, the lower limit of the luminance signal below a certain level is limited by the limiter circuit so that it reaches this level, or all input Add a constant to the luminance signal so that it does not fall below a certain level, so that the output signal of the division circuit will not become a value close to infinity, thereby preventing excessive correction of the color signal, and can Performs optimum image signal correction.

In addition, through the above structure, the APL is detected, and the correction amount adapted to the APL of the input image signal and the correction amount of the luminance signal is calculated to perform color signal correction, so that the optimum image signal correction compatible with the APL can be realized. .

Fig. 1 is a block diagram of a gradation correction device according to a first embodiment of the present invention.

Fig. 2 is a block diagram of a gradation correction device according to a second embodiment of the present invention

Fig. 3 is a block diagram of a gradation correction device according to a third embodiment of the present invention.

Fig. 4 is a block diagram of a gradation correction device according to a fourth embodiment of the present invention

Fig. 5 is a graph comparing the first and second embodiments of the present invention.

FIG. 6 is a block diagram of a conventional gradation correction device.

FIG. 7 is a waveform diagram illustrating the operation of a conventional gradation correction device.

Next, a first embodiment of the present invention will be described with reference to the drawings. In Figure 1, 1 is the luminance signal correction circuit, 2 is the contrast and brightness control circuit, 3 is the matrix conversion circuit, 4 is the CRT, 5 is the color demodulation circuit, 9 is the adder, 6 is the delay circuit, 7 is the division Circuit, 8 is a multiplication circuit, and the above structure is the same as that of Fig. 6. 100 is an APL detection circuit which detects the average luminance level of the input luminance signal. 101 is a coefficient calculation circuit, which calculates the APL detected by the APL detection circuit to obtain a correction signal suitable for the APL. 102 is an adder which adds the corrected luminance signal and the corrected signal based on APL. 104 is a limiter circuit, which limits the lower limit of the delayed luminance signal level. 105 is a coefficient control circuit, which controls the operation of the coefficient calculation circuit 101 and the limiter circuit 104 . In this example, each circuit from 100 to 105 can be constituted by an analog circuit, a digital circuit, or a combination of both.

Now, the operation of the image signal correction device configured as above will be described. First, the average luminance level p of the luminance signal a is detected by the APL detection circuit 100, and p is output. Furthermore, the coefficient calculation circuit 10 performs calculations, adds or subtracts a certain value to the APL signal p, multiplies the result by a certain factor, and outputs a correction signal q based on the APL.

In addition, the same corrected luminance signal b as in the conventional example is output from the luminance signal correction circuit 1 . Then, the corrected luminance signal b and the corrected signal q based on APL are added by the adder 102, and the corrected signal r is output.

On the other hand, the lower limit of the output signal l of the delay circuit 6 is limited by the limiter circuit 104 so that it cannot fall below a certain level, and it is output as the limit delayed luminance signal s. The division circuit 7 divides the correction signal r by the limit delay luminance signal s, and outputs the result to the multiplication circuit 8 as a color amplitude correction signal m.

The multiplication circuit 8 corrects the input color carrier signal d according to the color amplitude correction signal m.

The coefficient control circuit 105 controls the lower limit value of the clipping circuit 104 and the value of the coefficient calculation circuit 101 in relation to each other.

According to the above-mentioned embodiment, an APL detection circuit 100, a coefficient operation circuit 101, an adder 102, a limiter circuit 104, and a coefficient control circuit 105 are provided, so that the color signal can be corrected according to the APL, and at the same time, it can prevent when the input signal is low luminance The correction of the color signal is excessive at the level. The invention in turn can be implemented with smaller circuits.

Next, a second embodiment of the present invention will be described with reference to the drawings.

In Figure 2, 1 is the luminance signal correction circuit, 2 is the contrast and brightness control circuit, 3 is the matrix conversion circuit, 4 is the CRT, 5 is the color demodulation circuit, 9 is the adder, 6 is the delay circuit, 7 is the division Circuit, 8 is a multiplication circuit, 100 is an APL detection circuit, 101 is a coefficient operation circuit, 102 is an adder, and the structure above is the same as that of Fig. 1.

The difference from the structure of FIG. 1 is that a certain value is added to the delayed luminance signal by the second adder 103 .

Now, the operation of the image signal correction device configured as above will be described. First, the corrected luminance signal b is output from the luminance signal correction circuit 1 . In addition, the average luminance level p of the luminance signal a is detected by the APL detection circuit 100, and the coefficient calculation circuit 101 calculates the correction signal q based on APL based on this signal. Then, the first adder 102 adds the above-mentioned corrected luminance signal b to the corrected signal q based on APL, and outputs the corrected signal r. The above is the same as the first embodiment.

On the other hand, the output signal 1 of the delay circuit 6 is added with a certain constant by the second adder 103, and is output as a limit delayed luminance signal s.

The division circuit 7 divides the correction signal r by the limit delay luminance signal s, and outputs the result to the multiplication circuit 8 as a color amplitude correction signal m. The multiplication circuit 8 corrects the input color carrier signal d according to the color amplitude correction signal m.

According to the above embodiment, since the APL detection circuit 100, the coefficient calculation circuit 101, the first adder 102, and the second adder 103 are provided, color signals can be linearly corrected for the input luminance level according to the APL. Circuits can also be made on a smaller scale.

Next, a third embodiment of the present invention will be described with reference to the drawings.

In Figure 3, 1 is the luminance signal correction circuit, 2 is the contrast and brightness control circuit, 3 is the matrix conversion circuit, 4 is the CRT, 5 is the color demodulation circuit, 9 is the adder, 6 is the delay circuit, 8 is the multiplication Circuits, 100 is an APL detection circuit, 101 is a coefficient calculation circuit, 104 is a limiter circuit, 105 is a coefficient control circuit, the above structure is the same as that of Fig. 1.

The difference from FIG. 1 is that the first division circuit 7 performs division operation on the APL-based correction signal and the limit delayed luminance signal, and the second division circuit 110 performs division operation on the delayed luminance signal and the corrected luminance signal, and adds A device 111 adds the output signals of the above-mentioned first and second dividing circuits.

Now, the operation of the image signal correction device configured as above will be described.

First, the luminance signal correction circuit 1 outputs a corrected luminance signal b. Also, the APL detection circuit 100 detects the average luminance level p of the luminance signal a, and the coefficient calculation circuit 101 calculates a correction signal q based on APL based on the signal. Furthermore, the lower limit of the delayed luminance signal 1 is limited by the limiter circuit 104, and a limit delayed luminance signal S is output.

The coefficient control circuit 105 controls the lower limit value of the clipping circuit 104 in association with the value of the coefficient calculation circuit 101 . The above is the same as the first embodiment.

Next, the first dividing circuit 7 divides the APL-based correction signal q by the limit delayed luminance signal s, and outputs the result as a first correction signal u. On the other hand, the second dividing circuit 110 divides the corrected luminance signal b by the delayed luminance signal l, and outputs the result as a second corrected signal v. The adder 111 adds the first and second correction signals u and v to output a color amplitude correction signal m.

The multiplication circuit 8 corrects the color carrier signal d based on the color amplitude correction signal m.

According to the above-mentioned embodiment, the APL detection circuit 100, the coefficient operation circuit 101, the limiter circuit 104, the coefficient control circuit 105, the second division circuit 110 and the adder 111 are provided, so that the correction of the color signal can be carried out according to the APL, and the The ratio of the color signal correction amount to the luminance signal correction amount is kept constant.

Next, a fourth embodiment of the present invention will be described with reference to the drawings.

In Fig. 4, 1 is a luminance signal correction circuit, 2 is a contrast and brightness control circuit, 3 is a matrix conversion circuit, 4 is a CRT, 5 is a color demodulation circuit, 9 is an adder, 6 is a delay circuit, and 7 is a second circuit. 1 is a division circuit, 8 is a multiplication circuit, 100 is an APL detection circuit, 101 is a coefficient calculation circuit, 110 is a 2nd division circuit, 111 is a 1st adder, and the structure above is the same as in FIG. 3 .

The difference from FIG. 3 is that the second adder 103 adds a constant value to the delayed luminance signal.

Now, the operation of the image signal correction device configured as above will be described.

First, the luminance signal correction circuit 1 outputs a corrected luminance signal b. In addition, the APL detection circuit 100 detects the average luminance level p of the input luminance signal a, and the coefficient calculation circuit 101 calculates the APL-based correction signal q based on the signal. In addition, the second adder 103 adds a certain constant to the delayed luminance signal l, and outputs a limit delayed luminance signal s. The above is the same as the second embodiment.

Next, the correction signal q based on APL is divided by the limit delay luminance signal s by the first dividing circuit 7, and the result is output as the first correction signal u. On the other hand, the second dividing circuit 110 divides the corrected luminance signal b by the delayed luminance signal l, and outputs the result as a second corrected signal v. The adder 111 adds the first and second correction signals u and v to output a color amplitude correction signal m.

The multiplication circuit 8 corrects the color carrier signal d based on the color amplitude signal m.

According to the above-described embodiment, the APL detection circuit 100, the coefficient operation circuit 101, the second adder 103, the second divider circuit 110, and the third adder 111 are provided. Therefore, the color signal by APL can be corrected linearly with respect to the input luminance level, and the ratio of the correction amount of the color signal to the correction amount of the luminance signal can be kept constant at all luminance levels.

As described above, the present invention can realize a gradation correction device capable of correcting color signals based on APL by providing an APL detection circuit, a coefficient operation circuit, an adder, a clipping circuit, a division circuit, a multiplication circuit, and a coefficient control circuit. , which in turn prevents overcorrection of the color signal when the input signal is at a low luminance level.

In addition, the present invention can realize such a gradation correction device by arranging an APL detection circuit, a coefficient operation circuit, the first and second adders, a division circuit and a multiplication circuit, which can correct the color signal according to the APL, and can also compare the input brightness. The color signal is linearly corrected for the luminance signal.

In addition, the present invention can realize a gray scale correction device by setting an APL detection circuit, a coefficient operation circuit, a limiter circuit, the first and second division circuits, an adder, a multiplication circuit and a coefficient control circuit. Correcting the color signal also prevents overcorrection of the color signal when the input signal is at a low luminance level, and furthermore, corrects the color signal at the same rate as the correction rate of the luminance signal.

The present invention can realize a gray scale correction device by setting APL detection circuit, coefficient operation circuit, first and second adders, first and second division circuits and multiplication circuit, which can correct color signal according to APL, and can also The color signal is linearly corrected against the input luminance signal, and furthermore, the color signal can be corrected at the same ratio as the correction ratio of the luminance signal.

Claims (6)

1. An image signal correction device for correcting color signal saturation, characterized by comprising: A luminance signal correction circuit for correcting the grayscale of the input luminance signal; An average luminance level detection circuit for detecting the average luminance level of the luminance signal; A coefficient operation circuit for correction and calculation according to the output signal of the average luminance level detection circuit; an adder for adding the output signal of the above-mentioned luminance signal correction circuit to the output signal of the above-mentioned coefficient operation circuit; A delay circuit for delaying the above-mentioned luminance signal; A limiter circuit that limits the lower limit level of the output signal of the delay circuit; A division circuit that divides the output signal of the above-mentioned adder by the output signal of the above-mentioned limiting circuit; a multiplication circuit for controlling the amplitude of the input color carrier signal with the output signal of the above-mentioned division circuit; and and a coefficient control circuit that controls the coefficient calculation circuit and the limiter circuit. 2. An image signal correction device for correcting color signal saturation, characterized by comprising: A luminance signal correction circuit for correcting the grayscale of the input luminance signal; An average luminance level detection circuit for detecting the average luminance level of the luminance signal; A coefficient operation circuit for correction and calculation according to the output signal of the average luminance level detection circuit; a first adder that adds the output signal of the above-mentioned luminance signal correction circuit to the output signal of the above-mentioned coefficient operation circuit; A delay circuit for delaying the above-mentioned luminance signal; a second adder for adding the output signal of the delay circuit to a constant; The output signal of above-mentioned the 1st adder is divided by the division circuit of the output signal of the above-mentioned 2nd adder; A multiplication circuit for controlling the amplitude of the input color carrier signal by the output signal of the above division circuit. 3. An image signal correction device for correcting color signal saturation, characterized by comprising: A luminance signal correction circuit that receives a luminance signal and generates a corrected luminance signal, wherein the luminance signal correction circuit corrects the gray scale of the luminance signal; An average luminance level detection circuit that receives the luminance signal and generates an average luminance level signal at its output; A coefficient operation circuit connected to the output end of the above-mentioned average luminance level detection circuit, and the above-mentioned coefficient operation circuit generates a corrected average luminance level signal; a delay circuit receiving said luminance signal and generating a delayed luminance signal at its output; A luminance signal limiting device connected to the output of the delay circuit, the above-mentioned luminance signal limiting device generates a limited and delayed luminance signal higher than a specified level value; An adder that receives the corrected luminance signal and the corrected average luminance level signal and generates a corrected sum signal; a dividing circuit, connected to said adder and said luminance signal limiting means, for dividing said corrected sum signal by said limited and delayed luminance signal, generating at its output a color amplitude corrected signal; and A multiplication circuit that receives the input color carrier signal and is connected to the output end of the division circuit, and the color amplitude-corrected signal controls the amplitude of the input color carrier signal. 4. 3. The image signal correcting apparatus according to claim 3, wherein said luminance signal clipping means includes a clipping circuit for keeping said clipped and delayed luminance signal higher than a prescribed level. 5. The image signal correction device according to claim 3, wherein said luminance signal limiting means includes a second adder, and said second adder adds a predetermined constant value signal to said delayed luminance signal. , to keep the above-mentioned limited and delayed luminance signal above a specified level. 6. The image signal correction device according to claim 4, further comprising a coefficient control circuit connected to the coefficient calculation circuit and the limiter circuit, and the coefficient control circuit controls the lower limit of the limiter circuit in a mutual linkage relationship. Control with the coefficient value generated by the above-mentioned coefficient operation circuit.

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